Due to the frequency of injury to the anterior cruciate ligament (ACL), especially in sports, and similar injury to other ligaments and related structures, there is a great deal of prior art dealing with replacement of these structures with graft ligaments. Much of this prior art is concerned principally with ensuring proper alignment of bone tunnels drilled in the tibia and femur to receive the opposed ends of the graft ligament, preparation of the surgical site, i.e., by removing sufficient bone to allow the graft to function properly, and with preparation of suitable graft ligaments, commonly by harvesting donor bone/tendon/bone structures from the knee of the patient. See generally, "The Paramax ACL Guide System Surgical Technique", a brochure published by Linvatec Corporation of Largo, Florida in 1992, and incorporated by reference herein. Other sources of replacement ligaments, including allograft and autograft ligament substitutes, are within the skill of the art and are intended to be included within "graft ligament" as used herein.
The present invention does not address these aspects of ACL reconstruction, but instead addresses the problem of securely anchoring the graft ligament in the bone tunnels while properly tensioning the ligament so as to provide support for the joint.
The prior art also addresses the concerns of properly anchoring and tensioning the graft ligament. However, the prior art known to the inventor does not provide a fully satisfactory anchor mechanism whereby both ends of the graft can be anchored in opposed tunnels in the tibia and femur, followed by final adjustment of the ligament tension. That is, preferably the anchors (or other attachment means employed) at both ends of the graft ligament would first be secured in their ultimate positions, followed by final adjustment of the ligament tension, in order to provide proper joint articulation. To the limited extent the prior art provides this capability (see the discussion of Johnson U.S. Pat. No. 5,562,668 below), the anchor structures known are undesirably complex, bulky, and hard to use properly.
More specifically, a common prior art ACL replacement practice is described in U.S. Pat. No. 5,306,301 to Graf. A flat planar ligament anchor is first attached to the femur end of the graft ligament, and is passed upwardly from below, so as to pass entirely through bone tunnels formed in the tibia and in the femur; after the planar anchor exits the proximal end of the bore, it is turned so as to bear against the outer surface of the femur. The opposite end of the graft is then fixed to the tibia. No adjustment of the ligament tension is possible after the ends of the ligament graft are fixed.
This technique requires that the overall length of the assembly be determined accurately before the graft is fabricated and secured to the tibia and femur. A difference in the ligament length of as little as a few millimeters is critical in provision of correct joint articulation. However, measurements of this accuracy are very difficult to determine in advance, as there are many variables involved, including the relative depth to which the anchors will be inserted into the bone tunnels, and the working length of the graft ligament, which in turn will vary depending on the degree of tightness with which the ligament graft is sutured to the anchor(s), the degree of stretch in the ligament itself, and so forth. It would be far more satisfactory if the surgeon could simply fabricate the graft ligament to an approximate overall dimension, anchor both ends in their final positions, and then make final tension adjustments. This ability would simplify the surgical procedure and yield better joint articulation after repair.
As indicated above, U.S. Pat. No. 5,562,668 to Johnson teaches a tensioning device for ligament grafts. At least one end of the graft is fixed to a carrier having a screw-threaded cylindrical member extending toward the outer surface of the joint. The carrier is received by a nut in turn received within a thimble. After the carrier is threaded into the nut, a process which would appear difficult in practice, the nut can be turned further, drawing the carrier further into the thimble. The nut can only be turned using a special tensioning key, which must be hollow in order to pass a wire needed to make the initial assembly of the carrier to the nut.
While the Johnson structure would permit adjustment of the tension on the ligament after seating of the thimbles in the bone tunnels, the degree of adjustment provided is constrained by the linear extent of the thread formed on the carrier, in turn requiring relatively exacting measurement of the overall distance between the anchoring points, and necessitating that the length of the ligament be controlled to correspond to this distance, complicating the procedure. The Johnson assembly also includes a relatively large number of parts, requires a special tool, requires a relatively large-diameter bore in the bone to receive the carrier and thimble, and takes up a significant fraction of the distance between the anchors, reducing the overall length of the ligament itself.
Rosenberg U.S. Pat. No. 5,152,790 shows a relatively complex three-component anchor assembly for ACL reconstruction. A first of Rosenberg's components includes a shank having threads formed on its outer surf ace for engaging the bone, and having a smooth internal bore. Torque is transmitted to the first component by a second component having a bore with a cross-section suitable for receiving torque from an associated driver. The second component is laser welded or otherwise bonded to the first component in order that a third component, to which the ligament is affixed, can rotate with respect to the first and second components. In this way, the ligament to be fixed by Rosenberg's device is not twisted as the first threaded component is drawn into a bore in a bone by torque exerted on the bore of the second component.
Rosenberg's anchor can thus be threaded into a bore in a bone, but there is no separate adjustment provided for the tension on the ligament. For example, if the ligament is fully tensioned before the threaded component is seated properly, the procedure must be repeated. Of course, the other end of the ligament could be affixed only after the anchor attached to the first had been seated, but this would not allow tension adjustment after anchor securing, as desired. Rosenberg's anchor is also excessively complex and bulky.
Other prior art generally relevant to this invention includes U.S. Pat. No. 4,870,957 to Goble, disclosing tubular threaded anchors for insertion into bone tunnels, followed by insertion of snap-fitting securing members from the inside of the joint. Not only would this insertion step be rather difficult to perform, the tension adjustment possible thereafter would be constrained by the degree to which the anchors could be moved in the bone tunnels without disturbing their secure seating.
U.S. Pat. No. 4,772,286 to Goble (now Reissue Pat. No. 34,293) also discloses several embodiments of methods and anchor structures for ACL replacement. The anchors shown in FIGS. 2-5 of Goble are expanding conical structures. It appears that although these anchors are threadedly attached to the ends of the ligament graft, their relative position cannot be adjusted after the anchors are secured in their final position; that is, the threaded members are provided simply to ensure secure fixation of the anchors, and do not allow for subsequent tension adjustment.
In a second embodiment, shown in several variations in FIGS. 6-11, Goble teaches attaching the graft to the femur by threading a screw fixed to one end of the graft into a tunnel drilled in the femur; the opposite end is secured in the tibia by turning a conical nut threaded over a fitting at the tibia end of the ligament against a seat formed in the tibia. This again requires the tension adjustment and tibial securing of the ligament end to be accomplished simultaneously; that is, the surgeon does not have independent control of the securing of the graft ligament in the tibia and of ligament tension.
U.S. Pat. No. 5,643,266 to Li also shows anchors for ACL replacement or similar procedures involving expanding anchors. In Li, the tension on the ligament must be adjusted before the anchors are secured in place. See col. 6, lines 11-24. Hence the ligament tension may vary as the anchors are expanded and secured.
Treace U.S. Pat. No. 3,953,896 shows a prosthetic ligament assembly including opposed conical threaded nut members for securing the ends of a prosthetic ligament in bone tunnels, and sleeves for protecting the ligament against abrasion. Treace mentions (col. 4, line 48) that the tension on the ligament is adjusted by turning the nut members; it appears that the fit of the nut members on the bone tunnels would substantially limit the degree of adjustment provided.
Other patents generally relevant to the subject matter of this application include Greenfield U.S. Pat. No. 5,584,835, showing a device for affixing tissue to bone. A threaded bone anchor is first threaded into the bone; the soft tissue is then sutured to a suture anchor. The outer surface of the suture anchor and a recess in the bone anchor are provided with cooperating asymmetrical teeth, so that the suture anchor can readily be inserted into but is securely retained by the bone anchor. No provision is made for adjustment of tension in a soft-tissue structure thus affixed to bone.
U.S. Pat. No. 5,350,399 to Erlebacher shows a structure for sealing puncture wounds in blood vessels and the like wherein an intra-arterial occluder and an extra-arterial occluder are drawn toward and secured to one another by a sawtooth-shaped guide extending from the intra-arterial occluder, through the wound, and over which the extra-arterial occluder is placed; when the two are drawn together, the sawteeth on the guide prevent them from slipping apart. A tool is provided for drawing the guide out through the extra-arterial occluder while holding the latter in position.
Patents showing anchors for securing ligament ends and other tissue structure to bone that do not provide subsequent adjustment of tension include Morgan U.S. Pat. No. 5,603,716; Beck U.S. Pat. No. 5,632,748; Thein U.S. Pat. No. 5,356,435; Steininger U.S. Pat. No. 5,425,767; Silvestrini U.S. Pat. No. 4,708,132; Parr U.S. Pat. No. 4,744,793; Coleman U.S. Pat. No. 5,645,547; Goble U.S. Pat. No. 4,927,421; and others.